If you are jailbroken, you can. Full root access. Best is to NOT modify the root filesystem, but rather use "mount --bind" from your directory of files on top of the system directory.
https://www.mobileread.com/forums/sho...d.php?t=249137
http://docs.1h.com/Bind_mounts
Is this what you are asking? If you modify your root filesytem, it won't be very portable and an upgrade could easily wipe it out.
Good luck!